I did a search and can only find other threads about hoods or lots vanishing as a whole from the game, my problem is slightly different.
A couple of weeks ago, I downloaded one of psychosim's lots that she has at GoS -- the Winner Street batch. In one of them, Simford Prison, the lot worked just fine in build mode when I went to put in matching sidewalk and road tiles, I fixed a few blue objects (discussed at original GoS thread), saved and went back to the hood and moved my family in. The lot works great for a 5-10 minutes, and then whenever you tab out to get a choice pic, the lot vanishes and all you get is blue sky. If I zoom out, push "w" or "s", it'll show the street when you back up far enough, but on all the other sides the camera just skips over the building (it shows as blue sky) until you get past the lot and then it shows the grass and roads of the rest of the hood. I thought maybe it was a fluke the first time so I quit playing, tried again several times with the same result. It's only this lot, none of the others in my hood are acting this way. I have checked the cc in the folder and it's all pretty basic cc.

Any ideas on why my game does this and what I can do to make it stop???? The only thing that I thought was the problem was changing things in the lot while playing, but then it did it again when I left all as is after loading.